If there are 8 people together, it will be great fun, I prefer bike because you can experience everything which Came into your traveling and you can enjoy as much as you can with your friends, otherwise Indian railway is the best option from Hyderabad to NJP, after that you must hire a bike or car to travel further Sikkim is a beautiful place an lots of awesome views are waiting for you.
If 8 of you are friends then Google, read blogs and create your own itinerary. It will be fun and memorable instead of going with tours and travels. You might learn a lot about the places. Members here can give you numbers of friends in case you need help. Happy Holidays!
Don't book any packages for Darjeeling and Gangtok.
Book you flight or train to New Jalpaiguri. you can easily get share taxis to Darjeeling (Cost will be 300/400 per head. Book your Hotels via MMT..for local side seen, you can book cars and you will get contacts by your Hotels.